Conventionally, the polarized light color filter 10 is composed as illustrated in FIG. 1, and the video projector 12 incorporating such a polarized light color filter is composed as illustrated in FIG. 2.
More particularly, the polarized light color filter 10 is composed of a rotation axis 14 and a disk-shaped filter 16, which is securely fixed to the rotation axis 14, while the disk-shaped filter 16 is composed of three substantially equally portioned filters, namely, 16r, 16g and 16b for respectively transmitting the R-, G- and B-light components. The rotation of the rotation axis 14 causes the disk-shaped filter 16 to turn in the direction of the arrow; the white light (an example of the non-polarized light) is transmitted through the back side of the disk-shaped filter 16 so that the R-, G- and B-light (monochromatic light) areobtained on the time-division basis on the opposite side of the filter through the light transmission area matching with each of the R-light component, G-light component and B-light component transmission filters 16r, 16g and 16b. 
Further, in said conventional method, the video projector 12 obtains the three primary lights (R-light, G-light and B-light) on the time-division basis from the non-polarized light emitted from the white light source 20 by means of the polarized light color filter and separates the three primary lights into P-polarized light (denoted as P in the figure) and S-polarized light (denoted as S in the figure) by means of the polarized light beam splitter 22. Then, the P-polarized light is modulated by means of the front screen liquid crystal panel 24 (an example of reflection optical modulating element), and the reflected light (S-polarized light) is reflected by means of the polarized light beam splitter 22 to be projected on the screen through the projection lens 26 (not shown). In this case, when the front screen liquid crystal panel 24 is synchronized with the R-light, G-light and B-light, which are emitted from the polarized light color filter 10, the images carried by the R-light, G-light and B-light, are projected on the screen to form the colored image.
However, the conventional polarized light color filter 10 shown in FIG. 1 and the conventional video projector shown in FIG. 2 are known to have the following shortcomings.
(1) A mechanical element is necessary in order to rotate the disk-shaped filter 16, so that the mechanical vibration of the front screen liquid crystal panel 24 caused by the mechanical rotation makes the image on the screen less distinct due to the vibration transmitted to the screen. This tendency increases as the size of the filter becomes smaller. Besides, the dimensions of the filter tend to become larger relatively to the size of the actual light transmission area, thereby limiting the reduction of the size of the filter on the whole.
(2) The ratios of the R-light, G-light and B-light in a period are predetermined according to the ratios in the area of the R-light component, G-light component and B-light component transmission filter 16r, 16g and 16b, so that the ratios of the R-light, G-light and B-light cannot be varied freely during one given period.
(3) Since the switching among the R-light, G-light and B-light is made by mechanically rotating the disk-shaped filter 16, the rotating speed cannot be increased freely beyond the limit of the mechanical rotation.
(4) Since the switching among the R-light, G-light and B-light is made by mechanically rotating the diskshaped filter 16, the ratio of the light transmission area 18 for each of the filters 16r, 16g and 16bcorresponding to the R-light, G-light and B-light cannot be increased freely, thereby forcing the utilization rate per quantity of the light of the white light source 20 to be kept at a low level.
The present invention is made in consideration of the problems of the prior art as is described in the foregoing and is intended to provide a polarized light color filter, featuring substantially reduced dimensions, greater protection against the mechanical vibration, availability of free variation of the ratios among the R-light, G-light and B-light in a given period, speeding of the process for varying such ratios and the improved utilization rate per light quantity of the light source, as well as to providing a video projector incorporating such a polarized color filter.